Location set to UK but getting overseas clicks

Why when we have set all our ads to be UK or individual UK cities do we still get companies from India, China and Bangladesh being able to click on our adword? About half our paid traffic is being wasted on overseas companies researching us to sell their services!

Our campaign type is set to 'Search Network Only'. The reported 'clicks' from 'other locations' is zero however I know from the referral URL that these visitors are not from the UK and are clicking on ads.